If you are only concerned with changing the 'users' table name:
$config['tables']['users'] = 'customers';
And then just change the table name in your DB.
There is no configuration option to change the column name from 'id' to something else that I know of.
All of the Ion Auth methods are still going to use the "user" terminology though...as in delete_user, remember_user etc.
I personally would just leave it all as is unless there is some business need to change it to 'customers,' or if you already have a table called 'users' or something. The reason I say this is that having different table names and column names from Ion Auth just ends up in confusion when discussing with other developers or when reading back-and-forth in the model/config when working...but that is just my experience with it. It is open source after-all and the code is out there...you can change the whole thing if you like! :D